Laser temperature-jump apparatus for the study of force changes in fibers.

An iodine photodissociation laser generates the 1.315-micron infrared light used to heat the fiber and solvent. Heating of the cell contents by the direct absorption of laser energy is complete within the 100-microseconds rise time of the force transducer. A 5 degrees C temperature jump was usual. Interference with the force record by shock waves, electromagnetic disturbances, and uneven heating of fiber and solvent is minimal and close to the normal background noise of the transducer output. The postjump temperature of the cell remains static for a minimum of 400 ms before evidence of cooling is seen. The temperature of the cell could be changed rapidly. The cuvette contents could therefore be rapidly raised to, and lowered from, elevated prejump temperatures. As a result, sensitive biological samples are subjected to potentially denaturing conditions for the minimum length of time required for the temperature jump. Experiments on collagen and muscle fibers in which normal and rubber-like thermoelastic responses are kinetically resolved from each other are presented. The instrument offers substantial improvements in performance over other currently available designs.